Effects - Expend Once per Modifier?

[Jwguy]

So, making some effects for a player action while taking a break from other projects, and I noticed there is an Expend options labeled "Once Per Modifier". Does anyone know what this means? Surely the effect can't be expended multiple times, since one expense means that it is effectively removed.

EDIT: Tinkering with it a little, I found out it seems to remove only used modifiers, but leave the others effective until they are also used. Neat.